1,1,1- 1University of Bristol, School of Chemistry, United Kingdom of Great Britain – England, Scotland, Wales (s.khodia@bristol.ac.uk)
- 2Chemical Sciences and Engineering Division, Argonne National Laboratory, Lemont, Illinois 60439, USA (sjk@anl.gov)
The bimolecular reaction of Criegee intermediates (CIs) with esters of varying chain length and α-substitution have been investigated under atmospherically relevant conditions using laser flash photolysis combined with cavity ring-down spectroscopy (CRDS). The bimolecular rate coefficient for propyl formate reaction with the simplest CI (formaldehyde oxide) is about 300 times larger than those for methyl formate, ethyl formate, methyl acetate, and propyl acetate. The only structural difference between propyl formate and the other formates is the length of the alkyl chain, implicating the propyl group as a key factor in the observed rate enhancement.
The enhanced reactivity of propyl formate suggests that its extended chain facilitates a more favorable transition state via hydrogen bonding. In contrast, α-substitution with a methyl group in propyl acetate leads to a marked decrease in reactivity, indicating steric hindrance limits the reactive pathway. Interestingly, methyl trifluoroacetate bearing an electron-withdrawing CF3 group exhibits a rate similar to propyl formate (~10-12 cm3 s-1), likely due to stabilization of the transition state through enhanced charge separation.1 Smaller esters such as methyl formate react more slowly (~10-15 cm3 s-1). These results reveal a subtle interplay of hydrogen-bonding and steric effects in the 1,3 cycloaddition reaction of CIs and underscore the potential role of such reactions in secondary organic aerosol (SOA) formation and growth,2 expanding our understanding of CI-driven oxidation processes in the troposphere.
Figure 1. Laboratory generation and detection of CIs for bimolecular reaction rate measurements.
References
1 R. Chhantyal-Pun, M. A. H. Khan, C. A. Taatjes, C. J. Percival, A. J. Orr-Ewing and D. E. Shallcross, Int. Rev. Phys. Chem., 2020, 39 (3), 385-424.
2 R. Chhantyal-Pun, B. Rotavera, M. R. McGillen, M. A. H. Khan, A. J. Eskola, R. L. Caravan, L. Blacker, D. P. Tew, D. L. Osborn, C. J. Percival, C. A. Taatjes, D. E. Shallcross and A. J. Orr-Ewing, ACS Earth Space Chem., 2018, 2 (8), 833-842.
How to cite: Khodia, S., Garavagno, M. D. L. A., Klippenstein, S. J., and Orr-Ewing, A. J.: Role of H-bonding in Modulating Reactivity with Criegee Intermediates, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-11380, https://doi.org/10.5194/egusphere-egu26-11380, 2026.
